Of course not only Treser has built conversions. Some of the others can be found here. The list ist surely not complete and will be extended if I find more material.
So far, you can choose between:
ASC Cabrio
A convertible with folding roof using the Audi Coupe Type85.
Type 44 Camper
The Audi 100 family by Bischofberger using a Type44.
Type43 Camper
By Bischofberger, too...
Pininfarina Quartz
Coupe concept car by Pininfarina based on a Urquattro.
Sbarro Robur
Crazy show car by Franco Sbarro using Audi's turbo engine.
Desert Racer
Vantagefield built six desert cacers in 1994 upon Audi 80 B4s.
Audi 200 station wagon
Artz converted an Audi 200 Type43 to a station wagon...
Urquattro station wagon
...and did the same with a Urquattro, too.
V8 hearse
The last possibility to drive V8.
C4 hearse
Not as rare as the V8 hearse, but beautiful, too!
Italdesign Aztec
Sportscar with Audi engine and an extremely small production run.